Dry forming plant and method for dry forming a fibrous tissue using such dry forming plant

ABSTRACT

A dry forming plant is described which comprises at least one distribution unit having a fibre and air inlet. Such distribution unit is placed above a forming wire opposite to at least one vacuum box which is connected to a suction unit. The distribution unit has an open bottom for release of the fibre material onto the forming wire below the distribution unit. More rotating rollers having protruding spikes are provided in the distribution unit for covering the cross sectional area of the open bottom. The vacuum box is divided into at least three longitudinal zones in a direction transversal to the advance direction of the forming wire. Said longitudinal zones have upwardly orientated intakes arranged below the forming wire. The longitudinal zones are connected with the suction unit via an outlet. The outlet comprises first shut-off means for partly or totally closing the outlet. The first shut-off means are independently operable.

FIELD OF THE INVENTION

The present invention relates to a dry forming plant for dry forming of a fibrous tissue from a fibrous material chosen from amongst synthetic fibres and natural fibres, the dry forming plant comprises at least one distribution unit having a fibre and air inlet, and the at least one distribution unit being placed above a forming wire, the dry forming plant further comprises at least one vacuum box which is connected to a suction unit, and the at least one vacuum box being placed below the forming wire, wherein the at least one distribution unit has an open bottom for release of the fibre material onto the forming wire which is configured to be advanced below the distribution unit, and wherein one or more rotating rollers having protruding spikes are provided in the at least one distribution unit, the rotating rollers are arranged to cover the cross sectional area of the open bottom.

Furthermore the invention relates to a method of dry forming of a fibrous tissue from a fibrous material chosen from amongst synthetic fibres and natural fibres, using a dry forming plant.

BACKGROUND OF THE INVENTION

Various main distribution unit of this type are known, for instance from EP 0159618 B1. This application describes a main distribution unit provided with a bottom net or a sieve having a plurality of openings. In order to ensure the passage of the fibres through the bottom of the forming box it is suggested to use wings, rollers or other scraping or brushing devices, which in an active manner removes fibres from the sieve at the bottom of the main distribution unit. A vacuum box is provided underneath the forming wire for drawing the fibres through the bottom and onto the forming wire. Although such mechanical devices do give an increase in the capacity, the obtained increases are not satisfactory and attempts have been made through many years to increase the capacity further.

The size of the openings in the mesh or sieve in the bottom of the forming box is decided by the fibres, which are to be distributed on the forming wire. This is particularly relevant in relation to the use of cellulose fibres in the manufacture of paper products including absorbing products, such as napkins. Thus, there has been a limitation in the length of the fibres used.

In an attempt to overcome the problem with fibre length WO 99/36623 A1 describes a main distribution unit with an open bottom, i.e. without a bottom mesh or sieve. The distribution of fibres is carried out by a plurality of rotating spike rollers. Said spikes are arranged to partly hold the fibres back against the effect from the suction of the underlying vacuum box. The cloud of fibres which is formed inside the main distribution unit of single fibres, which are slit up and mixed in the air stream, are transferred down onto the underlying forming wire under the application of the rotating spike rollers. This increases the capacity of the forming apparatus significantly.

However, it has been discovered that agglomerates of fibres may pass the spike rollers without being torn sufficiently apart by the spikes, resulting in an uneven distribution of fibres on the forming wire and therefore in an inhomogeneous final product.

In order to overcome the problem with agglomerates of fibres EP 2078769 A1 describes a dry forming plant wherein the main distribution unit is divided into a plurality of interconnected distribution units each of which comprises at least one rotating roller, which are provided with protruding spikes.

By dividing the main distribution unit into a plurality of interconnected distribution units, it was possible to obtain a more efficient disintegration of fibres compared to the known main distribution units.

This is due to the fact that the disintegration of agglomerates shadows and/or lumps of fibrous material are influenced by strokes from spikes on the rotating rollers. When the spikes on the rotating roller impact with e.g. the agglomerates the impact force will ensure that said agglomerates are disintegrated. By having more than one distribution step it was found that agglomerates, shadows and/or lumps that are not disintegrated in the first distribution step will be disintegrated in the underlying distribution unit.

Hereby it was possible not only ensure, that all agglomerates, shadows and/or lumps in the fibrous material will be removed but also that the fibres will completely opened and separated. Hereby it was possible to produce uniform webs at higher speeds than heretofore possible and/or to improve the uniformity of webs made at existing speeds. It is assumed that the very high degree of separation caused by the different distribution steps improves the mixing of fibres in the main distribution unit to give these improved results.

However, the inventor has found that problems still occurred with variation of the thickness over the width of the product.

Also it has been found that problems may occur with variation of the properties of the product over the thickness of the formed.

Moreover the prior art dry forming plants according to either WO 99/36623 A1 or EP 2078769 A1 have a limitation in the width of the product to be formed. Even though the prior art dry forming plants makes it possible to produce uniform webs at high speeds then the variation of the thickness over the width of the product causes problems when a wide product is produced. Today there exist a desire to provide fibrous product with a width for up to 4000 mm or even wider, e.g. for providing backsides for carpets from fibres which may be chosen amongst synthetic fibres and natural fibres. Moreover such fibres may be long fibres compared to the traditionally cellulose fibres used in the manufacture of paper products including absorbing products, such as napkins.

Moreover, it is also a desire to use prior art dry-forming plants to the manufacture of insulation products. Such products will normally be produced from long fibers. The long fibers could have a length of 60 mm or more. Likewise it is a desire to use fibers which have a very inhomogeneous form and length in the product. Such fibers may e.g. be fibers from hemp plants. Such insulation mats may have a thickness up to 300 or even up to 500 mm or more.

Furthermore, even though it has shown possible to have a product with small variation of the thickness over the width of the product, there still exists problems with the uniform thickness at the side edges, especially when product having a lower thickness as low as 20 mm or lower. However problem with variations in side edges of the product is dependent on the fibre type and will also cause problems in product having a higher thickness.

The variation of the thickness over the width of the product causes a loss as side edges of the product need to be removed. The problem occurring at the side edges are in the prior art mentioned as “elephant foot”.

The prior art vacuum box according to WO 2004/065688 A1 comprises a suction area that is divided into a plurality of equally sized zones in the transverse direction and in longitudinal direction. Each column of suction zones in the longitudinal direction is connected to individual suction ducts which again are connected to individual fans. An electronic system is used to individually control the operations of the fan motors so that the suction in each longitudinal column can be varied. Each transverse row of suction zones are connected to manually operated shutter members so that the suction force can be increased as the product moves along the transport wire. A series of sensors are arranged downstream of the feeding head in order to detect the thickness or basis weight of the product, wherein the sensor signals are inputted to a control system for adjustment of the shutter members and fan motors.

However, problems with variations in side edges of the product may still occur. Because the suction zones are equally sized and equally distributed over the suction area, the vacuum box cannot be used to locally increase or close off the suction in the suction zones at the small area between adjacent distributor units. Therefore this vacuum box is not suited to be used in combination with multiple distribution units.

As it occurs from the above the prior art technology has given good results. However, it has shown that it is difficult to manufacture dry-forming plants having a substantial width and still maintain the uniform distribution over the width of the product—and also over the thickness of the product. Moreover, a substantial width of the dry-forming plant would cause problems with dimensions of the plant. For instance the dimensions of the rotating roller would have an increase in the diameter which may be more than double the diameter if the width of the distribution unit is increased.

There is a desire to provide the distribution units and possible also the vacuum box in a modular form and to arrange such modular form distribution units and vacuum boxes side-by-side in a direction transversal to the advance direction of the forming wire.

However, when placing more distribution units side-by-side transversal to the advance direction, the problems with variation of the thickness at the side edges of the product for each distribution unit will cause especial problems, seeing that such “side edges” may be places in an intermediate position over the width of the product produced. Accordingly, such variation is difficult to remove in the same way as it is removed when using just one distribution unit for the production of the product.

There is a desire to solve this problem.

OBJECT OF THE INVENTION

Thus, it is a first aspect according to the present invention to provide a dry forming plant which may use the technology disclosed in either WO 99/36623 A1 or EP 2078769 A1 in order to easily be adapted to different fibre types and fibre length and which ensures that variation in the thickness over the width of the product is obviated.

It is a second aspect according to the present invention to provide such dry forming plant in which it is possible to produce larger width than hitherto possible when using the technology disclosed in either WO 99/36623 A1 or EP 2078769 A1 and in which it is possible to obviate variation in the thickness over the width of the product.

It is a third aspect according to the present invention to provide a dry forming plant which is built in modular form in order to be able in easy way to produce products having different widths when using the technology disclosed in either WO 99/36623 A1 or EP 2078769 A1.

It is a forth aspect according to the present invention to provide a dry forming plant which makes it possible to produce a product in which variations of the properties of the product over the thickness of the product is obviated when using the technology disclosed in either WO 99/36623 A1 or EP 2078769 A1.

It is a fifth aspect according to the present invention to provide a dry forming plant which makes it possible to produce a product with a substantial thickness, which may be of the size of order of up to 400-500 mm when using the technology disclosed in either WO 99/36623 A1 or EP 2078769 A1.

It is a sixth aspect according to the invention to provide a dry-forming plant which makes it possible to produce a product with a substantial width, which may be of the size up to 4000 mm or wider, when using the technology disclosed in either WO 99/36623 A1 or EP 2078769 A1 when using modular elements for the building of the dry-forming plant.

It is a seventh aspect according to the present invention to provide a method of dry forming of a fibrous tissue from a fibrous material chosen from amongst synthetic fibres and natural fibres, using a dry forming plant using the technology disclosed in either WO 99/36623 A1 or EP 2078769 A1.

DESCRIPTION OF THE INVENTION

According to the present invention this is achieved with a dry forming plant disclosed by way of introduction and which is peculiar in that, each of the at least one vacuum box is divided into at least three longitudinal zones in a direction transversal to the advance direction of the forming wire, wherein the longitudinal zones have upwardly orientated intakes arranged below the forming wire, and wherein each of the longitudinal zones are connected with the suction unit via an outlet, the outlet comprises first shut-off means configured to partly or totally close the outlet, the first shut-off means are configured to be independently operated.

Each vacuum box forms a suction area extending in a transverse direction between opposite side edges and further in a longitudinal direction between a front edge and a back edge. The side edges define a total width of the suction area where the longitudinal zones each have a local width. Further, the front and back edges define a total length of the suction area where the transverse zones each have a local length.

Similarly, each distribution unit forms a distribution area extending in the transverse direction between opposite side edges and further in the longitudinal direction between a front edge and a back edge. The side edges define a total width of the distribution area and the front and back edges define a total length of the distribution area.

The inventor has found that it has been possible almost to eliminate variation in the thickness over the width of the product. When the vacuum box is divided into at least three longitudinal zones in the direction transversal to the advance direction of the forming wire it is possible to have at least two side zones located at the side edges of the vacuum box which may be orientated below the side edges of a distribution unit opposite the vacuum box.

Moreover, at least one central zone is provided. Seeing that the longitudinal zones are connected with outlet having first shut-off means it is possible to adjust the suction in the longitudinal zones and thus across the width of the web. The first shut-off means are preferably individually operated so that the suction can be adjusted independently in each longitudinal zone. Hereby it is possible to adjust the suction in such a way that problems with variation not only over the width but especially at the side edges are eliminated.

This is especially important for products with a limited thickness, however as mentioned above the variation is also dependent on the fibre type.

Moreover, the possibility of adjusting the suction in a longitudinal zone of the vacuum box which is situated below a side edge of a distribution unit is especially important when more distribution units are arranged side-by-side in a direction transversal to the advance direction of the forming wire. Hereby it is possible to obviate variations which occur at the side edge of the distribution, however, these areas in the product would be provided in an intermediate position over the width of the product when the product is formed in a plant having more modular distribution units arranged side-by-side.

It has shown advantageous to have a smaller side zone being arranged closest to a side edge of the vacuum box and then have a larger central zone being arranged next to the side zone. Preferably, a smaller side zone is arranged on either side of the larger central zone. The local widths of the side zones are smaller than the local width of the central zone. Alternatively or additionally, the local width of one side zone is larger than the local width of the other side zone.

Moreover, it has also shown that it is especially advantageous to have more than three zones. The central zone arranged between the side longitudinal zones would then be divided in at least one intermediate central zone arranged between at least two outer central zones. The outer central zones are further arranged next to the side zones. The outer central zones may be divided into further additional outer zones, if needed. Hereby an even more precise adjustment of the vacuum is possible by independently operable shut-off means associated with each of the longitudinal zones.

The intermediate and outer central zones may have equal local widths. Alternatively, the local width of the intermediate central zone may be larger than the local widths of the outer central zones, or vice versa. In a further alternative, the intermediate and outer central zones may all have different local widths.

When adding fibres to at least two distribution units arranged side-by-side in direction transversal to the advance direction it is especially important that a vacuum box arranged opposite to the distribution units would have a central zone in the area where adjacent sides of the distribution units are joined. Surprisingly, it has been found that the use of such central longitudinal zone with a uniform suction in the area where the side edges of the distribution units are joined has proved to give especially uniform thickness without variation in thickness. This has been surprising, however, it is believed that this uniformity and homogeneity of the thickness of the product in the area where two distribution units are joined is due to the fact that the suction caused by the vacuum box will cause in intermixing of fibres from the two side-by-side arranged distribution units.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that the longitudinal zones are divided into a number of transversal zones, where at least in a number of the transversal zones a second shut-off means is arranged, the second shut-off means is configured to partly or totally close the intake to that transversal zone, the second shut-off means at least in the advance direction are configured to independently operated.

As already mentioned a product having a substantial thickness may have variation of properties over the thickness. When further dividing the longitudinal zones into a number of transversal zones one obtain a vacuum box which at the upper side arranged closest to the forming wire would have a suction area divided into a grid having a number of intake orientated against the forming wire. All or some of the transversal zones provided in the longitudinal zones may be fitted with second shut-off means. The second shut-off means in each transversal zone may be operated independently so that it is possible to adjust the suction in the intakes as the web advances through the dry forming plant. Hereby it is possible to establish a lower suction at the beginning of the formation of the product and a higher suction when finishing the product just before it leaves the area below the distribution unit.

The transversal zones may all have equally local lengths. Alternatively, the transversal zones may all have different local lengths. Alternatively, the transversal zones may be arranged in groups where each group have different local lengths.

When the product is formed at the entry side of the distributing unit and only few fibres are placed on the forming wire a high air flow, a high suction force may cause different properties of the product in different layers seeing that some fibres may have a tendency to be sucked down by a higher suction force. When adjusting the suction force over the length of the distribution unit in the advance direction in a way where the increased thickness of the product is taken into account then it is possible to have more uniform suction effect on the fibres above the formed product. Hereby it has surprisingly shown that is possible to obtain a product with uniform properties over the thickness of the product.

It has been surprisingly found that the combination of individually controlling the suction in the longitudinal zones and individually controlling the suction in the transversal zones allows the dry forming plant to be easily adapted to different fibre types and fibre length.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that the longitudinal zones and transversal zones are formed by partitions plates provided with cut-outs arranged for joining the partitions plates.

When forming the longitudinal and transversal zones by partition plates it is possible to use thin plates. These plates are preferably made of metal and may be steel plates. Alternatively aluminium may be used. The plates can be provided with cut-outs. Such cut-outs can be formed for cooperation with each other whereby it is possible to join the partition plates in a direction perpendicular to each other in order to form the grid. The formation of cut-outs could be done with laser cutting or any other mechanical method. The formation of a grid by bringing cut-outs into engagement with each other is well-known. When having the cut-outs with a width corresponding to the thickness of a plate, the connection of the crossing plates would form an airtight connection.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that the outlet of the longitudinal zones are connected with suction tubes being directed in the advance direction.

As the longitudinal zones are directed in the advance direction for the forming wire it is especially beneficial that suction tubes are connected with the outlet to the longitudinal zones. One suction tube could be connected with more outlets as each outlet is independently operable. The suction tubes are preferably directed in the advance direction and arranged in a plane substantially parallel to the plane of the forming wire. Hereby the height of the plant is as low as possible compared to an outlet tube orientated in a downwardly oriented direction from the vacuum box.

When the suction tubes are arranged in the advance direction it is possible to provide the tubes in a position between the upper run of the forming wire and the lower run of the forming wire. When more suction tubes are arranged side-by-side it is possible to have different length of a first portion of the suction tubes and then having a bending of the suction tubes leading the tubes to suction units arranged at the side of the forming wire. The suction units may be arranged symmetrically at each side of the forming wire or be arranged only at one side of the forming wire. For larger width of the product it is preferred to use the symmetrically arrangement of the suction units. Alternatively, the suction units may be arranged at the front or back end of the dry forming plant which minimises the length of the suction tubes

The suction units may form an integrated part of the dry forming plant so that the plant has a compact configuration. The suction units may also be external suction units capable of being connected to the suction tubes via a coupling interface. The suction unit may be a fan driven by a motor, but other suction units may also be used.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that two or more independent distribution units are arranged side by side in direction transversal to the advance direction. According to a further embodiment according to the present invention the dry forming plant is further peculiar in that the vacuum box comprises a longitudinal zone in an area where adjacent sides of the two or more independent distribution units are joined and that the longitudinal zone is a central zone and at that at least one side zone is provided on each side of the central zone.

As already mentioned two or more independent distribution units could be arranged in modular form and be arranged side-by-side in direction transversal to the advance direction in order to increase the width of the product to be formed. It is possible to use one or more vacuum boxes arranged opposite the distribution units in a position below the forming wire. The vacuum box or vacuum boxes has/have a suction area corresponding to at least the distribution area of the distribution units.

When a longitudinal zone of the vacuum box is arranged in the area where adjacent sides of the distribution units are joined it is possible to have uniform distribution across the width when individually adjusting the suction to such central zone and side zones provided on each side of the central longitudinal zone.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that two or more independent vacuum boxes are arranged side by side in direction transversal to the advance direction. According to a further embodiment according to the present invention the dry forming plant is further peculiar in that the at least one vacuum box unit comprises an outermost side zone arranged at a side of the at least one vacuum box, the outermost side zone having a local width being smaller than a local width of another longitudinal zone of the at least one vacuum box.

The side zones arranged on each side of a central zone in the vacuum box(es) would normally—at the outermost side of the distribution unit or the outermost side of a number of distribution units arranged side-by-side—be sub-divided in such a way that it comprises an outermost longitudinal zone and at least one adjacent longitudinal zone.

As already mentioned the outermost side of the distribution unit(s) may be aligned with an outermost side zone arranged in the vacuum box(es). The outermost side zone preferably has a local width that is smaller than the local width of any of the other side zones. This makes it possible to more precisely adjust the suction in a longitudinal zone of the vacuum box which is situated below a side edge of the distribution unit. Hereby it is possible to obviate variations which occur at the side edge of the distribution.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that at least two of the distribution units and/or the vacuum boxes provided in the dry forming plant are either identical or symmetrical.

It is convenient to establish a plant by using modular distribution units. Such modular distribution units could be identical and be arranged with an independent fibre and air inlet. Alternatively the distribution units may be symmetrical, e.g. be a mirror image of each other. It is known from prior art that a distribution unit would be provided with a flow of air-born fibres which are led into the distribution units with an overpressure. Accordingly, the fibres and air inlet would be identical for each of the distribution units in a dry-formed plant having more distribution units arranged side-by-side.

Alternatively, it is possible to have one common tube with fibre and air which are connected to individual fibre and air inlets associated with each of the distribution units.

When providing air it is normal that the volume of air supplied to the distribution unit should be adjusted according to the pressure in the vacuum box. Hereby it is possible that the air entered into the distribution unit is balanced with the amount of air being removed by the suction effect of the vacuum box.

It has shown that it is difficult to adjust this pressure precisely.

If a higher airflow is entered into the distribution unit than is removed by the vacuum box then turbulence occurs within the distribution unit which may damage the uniformity of the product formed.

According to the present invention it is therefore preferred that a false drag of air is established whereby the vacuum box would remove more air than entered through the fibre and air inlet. This is obtained by providing the distribution units with adjustable plates arranged at the bottom of the plates at the entry side of the distribution unit and the outlet side as seen the advance direction of the forming wire. By adjusting such plates by a sliding movement in upwardly direction it is possible to establish a gap which makes it possible that a higher volume of air is removed through the vacuum box than the amount of air entered into the distribution unit in the combined fibre and air inlet.

With such solution the risk of turbulence is obviated and the product will occur with more uniform structure.

In the same way as modular distribution units are possible to use then also modular vacuum boxes could be provided side-by-side in direction transversal to the advance direction. Such vacuum boxes would each comprise an independent outlet for connection to a suction unit. Each vacuum box could be associated with its own suction unit or could be connected to a common suction unit through a manifold.

It should be realised that each vacuum box will be divided into longitudinal zones as already explained and that each longitudinal zone would be connected with the first shut-off means. The first shut-off means are arranged for independently operation of the outlet to each of the longitudinal zones. Even if more vacuum boxes are arranged side-by-side, then the longitudinal zones in each of the vacuum boxes would be associated with first shut-off means which are independently operable for each of the longitudinal zones. Such modular vacuum boxes could be identical or be symmetrical, e.g. be a mirror image of each other.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that the first shut-off means for each of the longitudinal zones are slide valves and that each is connected with independent operable first operation units.

It is preferred that the first shut-off means are slide valves which each is connected with a first operation unit in order to be independently operable. Alternatively, the shut-off means could be other form for valves, e.g. rotating valves or could be also be dampers which are rotating.

The slide valves are preferred, seeing that they are a technical simple construction which makes it possible to establish the individual operation of each longitudinal zone within a limited space.

According to a further embodiment according to the present invention the dry forming plant is peculiar in that the second shut-off means for the one transversal zone are rotary dampers which are mounted on a common pivotally mounted shaft being connected with independent operable second operation units.

The second shut-off means are preferred to be rotary dampers which are arranged inside the intake which are provided the grid formed by the partition plates. The second shut-off means will be arranged on a common pivotally shaft which is extending across the width of the vacuum box. Hereby only one second operation unit is needed for a row of second shut-off means arranged side-by-side across the width of the vacuum box.

This is a convenient construction as there is a limited space in the area between the upper run and the lower run of the forming wire where the vacuum box is arranged. Accordingly, the second operation unit could be arranged outside the forming wire. Accordingly, they could be easy to adjust and to maintain.

Alternatively, it is possible that each rotary damper for each intake formed in the grid could be independently operable. However, there is a limited need for such independent operation of each second shut-off means. The use of the second shut-off means for the transversal zones is used for obviating the risk of different properties over the height of the product. As explained above it is therefore important that the second shut-off means are used for adjusting the suction to be effected over the length of the distribution unit as seen in the advance direction for the forming wire.

Accordingly, it is preferred that a row of second shut-off means arranged in transversal direction would be operated by one second operating unit.

The method according the invention is peculiar in the steps of:

-   -   feeding at least one fibrous material into at least one         distribution unit,     -   establishing a suction through a forming wire via at least one         vacuum box,     -   distributing the at least one fibrous material from the at least         one distribution unit onto the forming wire, and     -   advancing the forming wire during the distribution of the         fibrous material to form the fibrous tissue.

As mentioned earlier, the inventor has found that it has been possible almost to eliminate variation in the thickness over the width of the product using the present invention. This allows for an improved dry forming process of fibrous webs as the suction is able to be precisely adjusted in critical areas, such as at the side edges and the area between adjacent distribution units. The present invention also allows the dry forming plant to be easily adapted to produce webs/tissues made from different fibrous materials or a mixture thereof.

The method according the invention is peculiar in that the at least one fibrous material is fed to at least two distribution units arranged side by side in direction transversal to the advance direction, where a local suction is provided in a central zone in an area where adjacent sides of the two distribution units are joined, and where the local suction is independently controlled in relation to a local suction provided in at least one side zone arranged on each side of the central zone.

As mentioned earlier, it has been surprisingly found that by preforming an individual control of the local suction in such central zone relative to the local suctions in the adjacent side zones it is possible to obtain a uniform thickness in the production without variation. The local suction provided by this central zone is likely to cause an intermixing of fibres from the two side-by-side arranged distribution units.

The method according the invention is peculiar in that a local suction is provided in an outermost side zone arranged at an side edge of the at least one vacuum box, and where the local suction is independently controlled in relation to a local suction provided in at least one side zone arranged adjacent to the outermost side zone.

Alternatively or additionally, it has been surprisingly found that by preforming an individual control of the local suction in such outermost side zone relative to the local suctions in the adjacent side zones it is possible to better control the thickness of the product at the side edges. It is thus possible to significantly reduce the problems with variations in the side edge areas of the product.

DESCRIPTION OF THE DRAWING

The invention will now be explained in further detail with reference to the accompanying schematic drawing, wherein

FIG. 1 is a schematic perspective view of an embodiment of a prior art dry forming plant forming a part of the present invention,

FIG. 2 is a schematic perspective view of an embodiment of a plant according to the present invention,

FIG. 3 a partial schematic view of the plant illustrated in FIG. 2,

FIG. 4 a partial side view of the plant illustrated in FIG. 2,

FIG. 5 a partial view of a vacuum box of the plant illustrated in FIG. 2,

FIG. 6 a perspective view of the vacuum box with partition plates mounted for defining a grid of intake openings,

FIG. 7 a view of the vacuum box provided with suction tubes and rotary dampers arranged in the intakes,

FIG. 8 a side view of the vacuum box illustrating sliding plates establishing a gap for false drag,

FIG. 9 a side view seen from the opposite side illustrating the slide plates and the rotary dampers in a vertical position leaving the intakes open,

FIG. 10 a perspective sketch illustrating the principle of a first modular construction of the plant,

FIG. 11 a perspective sketch illustrating the principle of a second modular construction of the plant,

FIG. 12 a perspective sketch illustrating the principle of a second modular construction of the plant,

FIG. 13 a perspective sketch illustrating the principle of a fourth modular construction of the plant,

FIG. 14 a perspective sketch illustrating the principle of a construction of the plant, and

FIG. 15 a schematic view illustrating how a product is built on a forming wire below a distribution unit.

DETAILED DESCRIPTION OF THE INVENTION

In the explanation of the Figures, identical or corresponding elements will be provided with the same designations in different Figures. Therefore, no explanation of all details will be given in connection with each single Figure/embodiment.

In the following it is assumed by way of example that a main distribution unit according to the invention comprises four distribution units. This is not limiting the invention. The main distribution unit can comprise from one to a plurality of distributions units.

In FIG. 1 a main distribution unit 1 according to prior art is shown. The main distribution unit comprises four independent interconnected distribution units 2, 3, 4 and 5 respectively. Fibres are supplied to the first distribution unit 2 via an inlet 6. A vacuum box 7 is positioned beneath a forming wire 8, and the main distribution unit is positioned above the wire. Hereby suction is established through the forming wire and fibres 9 are air laid on the forming wire 8 to form a web 10 in a dry forming process. Only an upper run 22 of the forming wire 8 is illustrated in FIG. 1. The forming wire is an endless wire belt.

In FIG. 1, the main distribution unit is shown with the interior elements visible in the fourth distribution unit 5. However, it is realized that the housing walls may be made from transparent or opaque materials.

Inside each distribution unit 2, 3, 4, 5 rotating rollers are provided with protruding spikes 12.

In the embodiment shown in FIG. 1 the first distribution unit 2 comprises one rotating roller 11, the second distribution unit 3 comprises two rotating rollers 13, 13, the third distribution unit 4 comprises one rotating roller 14, and the forth distribution unit 5 comprises five rotating rollers 15, 16, 17, 18, 19, placed in a substantially horizontal plane parallel to the forming wire 8.

The five rotating rollers 15, 16, 17, 18, 19, which are placed within the forth distribution unit 5, can be said to make up the bottom of the main distribution unit wherein three rotating rollers 15, 16, 17 are placed by one side wall of the distribution unit and two rotating rollers 18, 19 at the opposite side.

It will be evident for the person skilled in the art that the number of rotating rollers can be adjusted depending on the desired product and the fibres used.

Motors 20, arranged with the possibility for a variable rotation rate, drives each rotating roller, ensuring that it is possible to adjust the revolution rate of the engines dependent of choice of rollers, spikes and the product, which is to be formed.

Each of the rotating rollers 11, 13, 14, 15, 16, 17, 18, 19 has an axle 21, upon which spikes 12 in form of thread-formed elements are protruding. The spikes 12 are established with a size and a mutual distance, which makes it possible to allow for a passage in-between for corresponding spikes 12 on a neighboring rotating roller.

The rotating spike rollers are in the embodiment shown in FIG. 1 placed so that the outer ends of the spikes describe circles that do not overlap each other but can within the scope of the invention also be meshing like toothed gear or touch each other during the rotation.

The fibres 9 are supplied to the main distribution unit 1 via inlets 6. Said fibres will comprise agglomerates, lumps and/or shadows and when these comes into contact with the spikes 12, the agglomerates, lumps and/or shadows will be disintegrated or shred in order to ensure an even distribution of fibres 9 in the product 10 formed on the forming wire 8.

This is due to the fact that the disintegration of agglomerates of a fibrous material are influenced by strokes from spikes on the rotating rollers, and when e.g. an agglomerate is hit by a rotating spike the impact force will ensure that the agglomerate, at least to some extent, will be forced to open and/or disintegrate.

As this is repeated, not only several times in each distribution unit, but also in the four distribution units, all agglomerates, shadows and/or lumps will be removed in order to ensure an even distribution of fibres 9 in the product 10 formed on the forming wire 8.

The closer the spikes 12 are placed to each other on the rotating rollers 11, 13, 14, 15, 16, 17, 18, 19, the more efficient will the spikes return agglomerates, lumps and/or shadows to the respective distribution units 2, 3, 4, 5. In this manner the fibre clumps or clusters of fibres are retained by the rotating rollers and separated or disintegrated in a graduated fashion as these retained fibres are returned by the spikes 12 to the distribution unit rather than being sucked down to the forming wire 8 or underlying distribution unit by the vacuum box 7.

Fibres are supplied in an airflow to the first distribution unit 2 via an inlet 6. The airflow can be created by means of transport blowers, which are linked with pipes that lead to the distribution unit, but other ways of obtaining the airflow known to the person skilled in the art are within the scope of protection.

In the embodiment shown in FIG. 1 the fibres are primarily led in from each side of the first distribution unit 2, but fibres could also be feed to the distribution unit by means of more inlet pipes on each side of said distribution unit or to several of the distribution units. It is hereby possible to vary the capacity of the main distribution unit by opening and closing the inlet pipes.

As an alternative to the inlet 6 the fibres can be introduced to the main distribution unit in question by blowing them into said main distribution unit. This will ensure, that the fibres have a substantial velocity upon introduction to the unit, which provides that large concentrations variations throughout the main distribution unit will be reduced or even eliminated, ensuring a more uniform distribution of small fibres in the web. In case the product shall be provided with super absorbents or other powder products a more uniform distribution of such powder products is obtained.

The topmost first distribution unit 2 may or may not have a detachable lid 23 to allow inspection and maintenance of the main distribution unit, and to provide the possibility of admitting false drag so that a negative pressure does not build up in the main distribution unit and obstructs the continuous flow towards the forming wire obtained by means of the vacuum box 7. Preferably, the lid 23 has an air inlet opening 24 for admitting the false drag. The opening may be provided in the lid 23 or any other suitable site on the main distribution unit, e.g. in the axial side of the first 2 and/or subsequent distribution unit, as well as more openings may be provided and favorable. The openings for false drag may also be a gap at the bottom of the main distribution unit, which gap may be adjustable.

The uniform distribution is furthermore increased as the rotating rollers retain fibres before they are gradually sucked down via the vacuum from the vacuum box to the forming wire. In this way the rotating rollers works as a kind of buffer zone, ensuring, that the fibres do not fall directly onto the forming wire.

Fibres or other product which are to be part of the final web could also be are added to several of the distribution steps of the main distribution unit according to the invention, increasing the capacity of the main distribution unit.

In this respect the fibre material comprising the agglomerates, lumps and/or shadows which requires the highest impact force can be feed to the first distribution unit 2, and the fibre material which requires the lowest impact force to the forth distribution unit 5.

FIG. 2 illustrates a dry forming plant having two distribution units 1 arranged side-by-side in direction transversal to the advance direction 26 for the forming wire 8.

The distribution unit which may be called a main distributor unit comprises a number of independent distribution units. This is in accordance with the explanation in connection with FIG. 1. However, in the following the mentioning of a distribution unit would correspond to the main distribution unit explained in connection with FIG. 1.

The two distribution units 1 are identical and are arranged side-by-side in order to increase the width of the product 10 formed on the forming wire 8.

In the following there is an explanation of one distribution unit 1, however, it is clear that the explanation will be valid for both distribution units 1 illustrated in FIGS. 2-4.

FIG. 2 illustrates a plant according to the present invention and here it is seen that the former wire 8 has an upper run 22 and a lower run 25. The forming wire 8 has a movement in direction of the arrow 26.

The vacuum box 7 is arranged in the area between the upper run 22 and the lower run 25 of the forming wire 8. The vacuum box 7 is through funnels 27 (see FIG. 7) connected with suction tubes 28. The suction tubes 28 extend in the advance direction 26 of the upper run 22 of the forming wire 8. The suction tubes 28 (see FIG. 7) have a bend 29 (see FIG. 7) and are connected with further suctions tubes 30 extending transversal to forming wire 8 where the tubes 30 are connected with suction units in form of suction fans 31 arranged at the side of the forming wire 8.

The suction fans 31 may be connected with the inlets 6 for the distributor unit 1.

FIGS. 3, 8 and 9 illustrate partial views. A number of elements are not shown for clarity. E.g. only one row of motors 20 for the rotating rollers is illustrated. The distribution unit 1 is disclosed with a fiber cloud box 32 arranged above the distribution unit 1.

The distribution unit 1 comprises at the inlet side 33 a sliding plate 34 which is used for establishing a gap 35 beneath a lower edge of the sliding plate 34 and the upper run 22 of the forming wire 8. Hereby a possibility for false drag is established. This could be instead of the false drag through an opening 24 and/or be a further possibility for establishing false drag.

A sliding plate (not illustrated) corresponding to the sliding plate 34 is arranged at the outlet side 37 of the distribution unit 1 in order to adjust a gap (not visible) arranged at the outlet side 37 of the distribution unit 1.

In FIG. 8 the vacuum box 7 1 is illustrated from one side, and in FIG. 9 the vacuum box 7 is illustrated from the other side, however, with the side plate removed whereby the interior of the vacuum box is visible. Hereby it is possible to see rotary dampers 39 which each are arranged on a common pivotally mounted shaft 40. The pivotally shafts 40 are independently operable by means of second operating units (not shown) associated with each of the shafts 40. The second operating units may be a rotary actuator or any other suitable actuation means, e.g. a handle that is manually operated.

The distribution unit is not illustrated. It will be arranged over the vacuum box 7 illustrated in FIGS. 8 and 9.

FIG. 4 illustrates an end view of the dry forming plant illustrated in FIG. 3. FIG. 4 illustrates the sliding plates 34 arranged in an upper respectively a lower position above the forming wire 8. The sliding movement is established as the plate 34 is provided with slits 41 cooperating with screws 42 which may be loosened and tightened for sliding and fixing the sliding plates 34 in any position.

Instead of using one sliding plate 34 for a distribution unit 1 it is possible to use two or more sliding plates.

FIG. 5 illustrates a vacuum box 7 used in the dry-forming plant illustrated in FIGS. 2-4.

The vacuum box 7 is divided into longitudinal zones 43 arranged side-by-side in a direction transversal to the advance direction 26. Accordingly, each of the zones 43 extends in direction of the advance direction 26.

The longitudinal zones 43 are established by longitudinal partition plates 44 which are provided with cut-outs 45 extending partly over the height of the longitudinal partition plate 44. Hereby transversal partition plates 46 having corresponding cut-outs 47 for engagement with the cut-outs 45 can be arranged perpendicular to the longitudinal partition plates 44 in order to form a grid of individual intakes 48. Only a part of the intakes are illustrated for illustrative purpose.

The longitudinal partition plates 44 provided with openings 49 for passage of the common pivotally shafts 40 for the rotary dampers 39.

From FIG. 5 it seen that rotary dampers 39 are provided in the different intakes 48 of the grid formed by the crossing partition plates 44, 46. The intakes 48 are directed upwardly against the forming wire and are arranged below the upper run of the forming wire.

The longitudinal zones 43 are connected with the suction units 31 via an outlet 36 for each of the longitudinal zones 43. In each of the outlets 36 cut-off means in form of slide valves 50 are arranged. Hereby it is possible partly or totally to close the associated outlet 36. The slide valves 50 are independently operable by means of first operating units (not shown) associated with each of the slide valves 50. The first operating units may be a linear actuator or any other suitable actuation means.

As it occurs from the above it is possible to adjust the vacuum and thereby the suction established in each of the longitudinal zones 43 with the operation of the slide valves 50. Moreover, it is possible to adjust the vacuum and thereby the suction established in each intake 48 of the grid by operating the rotary dampers 39.

Accordingly, it is possible to establish a very precise adjustment of the suction force in different areas of the grid formed at the upper side of the vacuum box 7.

The vacuum box 7 is divided into at least three longitudinal zones 43.

FIG. 6 illustrates the vacuum box 7 according to FIG. 5 including all longitudinal partition plates 44 and all transversal partition plates 46. For clarity the rotary dampers and the slide valves are not illustrated in FIG. 6.

The embodiment illustrated in FIG. 6 is divided into seven longitudinal zones 43. The embodiments are divided into six transversal zones 51 by means of the transversal partition plates 46.

Hereby the grids of intakes 48 are established. One could say that each intake is provided in a crossing area where a longitudinal zone and a transversal zone are crossing.

The vacuum box illustrated in FIGS. 5 and 6 is intended for being arranged below the two distribution unit 1 arranged side-by-side in direction transversal to the advance direction 21.

In FIG. 4 it is illustrated that the vacuum box 7 is divided into the seven longitudinal zones 43. Lines 52 illustrate the position of the longitudinal partition plates 44. From FIG. 4 it is seen that a central zone denoted 54 is arranged in the vacuum box in an area 75 where adjacent sides 76 of the two distribution unit 1 are joined.

Turning to FIG. 6 it is visible that the vacuum box 7 comprises a first side zone 55 on each side of the central zone 54. Moreover, it is seen that a second side zone 56 is also arranged in a more outwardly position compared to the central zone 54. Finally, it is also seen that an outermost side zone 57 is arranged at each side of the vacuum box 7.

As already explained above the dry-forming plant may be provided in modular form. Accordingly, modular distribution units 1 may be used.

These modular distribution units 1 can be used together with one single vacuum box 7 or together with a number of modular vacuum boxes 7 arranged side-by-side in a direction transversal to the advance direction 26.

FIG. 10-14 illustrate different embodiment for a dry-forming plant manufactured of a modular set of distribution units 1 and vacuum boxes 7. Other combinations than the illustrated combinations are possible. The partitions plates in the vacuum boxes 7 are not illustrated. However the partition plates will be arranged according to the principles described above.

FIG. 15 illustrate a different embodiment for a dry-forming plant manufactured of only one distribution unit 1 and one vacuum box 7.

In FIGS. 10-14—and also in FIG. 15 only the distribution units 1 and the vacuum boxes 7 are illustrated for clarity.

FIG. 10 illustrates two identical distribution units 1 arranged in a position above one vacuum box 7. The vacuum box is divided into three longitudinal zones 43 and comprises a central zone 54 arranged below the area 75 where sidewalls 76 for the distribution units are combined. On each side of the central zone 54 a side zone 56 is arranged. Furthermore, outermost side zones (not illustrated here) are provided at the outermost sides of the vacuum box 7.

FIG. 11 illustrates a different embodiment having three identical distribution units 1 arranged side-by-side in a position above to two identical vacuum boxes 7 which are also arranged side-by-side. Instead, the two vacuum boxes 7 may be symmetrically arranged around the adjoining sides. Here the longitudinal zones are not illustrated.

FIG. 12 illustrates a further embodiment which also has three identical distribution units 1 arranged side-by-side in a position above four identical vacuum boxes 7 which are also arranged side-by-side.

FIG. 13 illustrates a further embodiment where three identical distribution units 1 are arranged side-by-side. Below the distribution unit five identical vacuum boxes 7 are arranged.

When using more than two vacuum boxes 7 arranged side-by-side, then the outermost side zone 57 needs only to be provided at the two outermost sides of the vacuum boxes arranged side-by-side. Such outermost side zone 57 is intended for overcoming problems with “elephant foot” in the outermost edge area of the product 10 formed closest to the outermost side of the distribution unit.

However, all vacuum boxes 7 can be identical, seeing that the control of the vacuum established in each of the longitudinal zones 43 can be adjusted. The adjustment may be effected in such a way that an outermost side zone 57 of a vacuum box 7 arranged in an intermediate position in the row of side-by-side arranged vacuum boxes 7 may be controlled in the same manner as a neighboring longitudinal zone 43.

FIG. 14 illustrates one distribution unit 1 arranged in a position above one vacuum box 7. The vacuum box 7 comprises a central zone 54 and on each side of the central zone 54 a side zone 55 is arranged. Furthermore, outermost side zones 57 are provided at the outermost sides of the vacuum box 7. The outermost zones 57 have a smaller local width than the local width of the side zones 55. Further, the central zone 54 has a smaller local width than the local width of the side zones 55.

FIG. 15 illustrates the formation of the product 10 formed on the forming wire 8. It is seen that the product has very low height at the inlet side 33 of the distribution unit 1 and have a larger height at the outlet side 37 of the distribution unit 1. In order to establish a uniform suction force over the length of the product arranged below the distribution unit 1 the rotary dampers 39 are arranged under different angles.

In FIG. 15 a smoothening roller 58 is illustrated. This smoothening roller 58 may be provided for establishing a smoothening of the surface of the product 10. 

1. A dry forming plant for dry forming of a fibrous tissue from a fibrous material chosen from amongst synthetic fibres and natural fibres, the dry forming plant comprises; a forming wire; at least one distribution unit having a fibre and air inlet, and the at least one distribution unit positioned above the forming wire, a suction unit; at least one vacuum box connected to the suction unit, the at least one vacuum box positioned below the forming wire; wherein the at least one distribution unit includes an open bottom configured and arranged to release the fibre material onto the forming wire which is configured and arranged to be advanced below the distribution unit; and one or more rotating rollers having protruding spikes are provided in the distribution unit, the one or more rotating rollers are configured and arranged to cover the cross sectional area of the open bottom, wherein each of the at least one vacuum box is divided into at least three longitudinal zones in a direction transverse to an advance direction of the forming wire, and wherein the at least three longitudinal zones have upwardly orientated intakes arranged below the forming wire, and wherein each of the at least three longitudinal zones are connected with the suction unit via an outlet, each of the outlets include first shut-off means configured and arranged to partly or totally close the respective outlet independent of the other outlets.
 2. The dry forming plant according to claim 1, wherein the at least three longitudinal zones are divided into a number of transverse zones, wherein at least one of the transverse zones includes a second shut-off means, the second shut-off means are configured to partly or totally close the respective intake to that transverse zone independent of the other intakes at least in the advance direction.
 3. The dry forming plant according to claim 2, wherein the longitudinal zones and transverse zones are formed by partition plates provided with cut-outs configured and arranged for joining the partition plates.
 4. The dry forming plant according to claim 1, wherein the outlet of the longitudinal zones are further connected with the suction unit via suction tubes directed in the advance direction.
 5. The dry forming plant according to claim 1, wherein the at least one distribution unit includes two or more independent distribution units arranged side by side in a direction transverse to the advance direction,
 6. The dry forming plant according to claim 5, wherein the at least one vacuum box comprises a longitudinal zone in an area where adjacent sides of the two or more independent distribution units are joined, the longitudinal zone is a central zone and at least one side zone is provided on each side of the central zone.
 7. The dry forming plant according to claim 1, wherein the at least one vacuum box includes two or more independent vacuum boxes arranged side by side in a direction transverse to the advance direction.
 8. The dry forming plant according to claim 1, wherein the at least one vacuum box unit comprises an outermost side zone, the outermost side zone having a local width being smaller than a local width of another longitudinal zone of the at least one vacuum box.
 9. The dry forming plant according to claim 1, wherein at least two of the distribution units and/or the vacuum boxes are either identical or symmetrical.
 10. The dry forming plant according to claim 1, wherein the first shut-off means for each of the longitudinal zones are slide valves connected with independently operable first operation units.
 11. The dry forming plant according to claim 2, wherein the second shut-off means for the at least one transverse zone are rotary dampers mounted on a common pivotally mounted shaft connected with independently operable second operation units.
 12. A method of dry forming a fibrous tissue from a fibrous material chosen from amongst synthetic fibres and natural fibres, using a dry forming plant according to claim 1, wherein the method includes the steps of: feeding at least one fibrous material into at least one distribution unit, establishing a suction through a forming wire via at least one vacuum box, distributing the at least one fibrous material from the at least one distribution unit onto the forming wire, and advancing the forming wire in an advance direction during the distribution of the fibrous material to form the fibrous tissue.
 13. The method according to claim 12, wherein the at least one fibrous material is fed to at least two distribution units arranged side by side in a direction transverse to the advance direction, where a first local suction is provided in a central zone where adjacent sides of the two distribution units are joined, and where the first local suction is independently controlled in relation to a second local suction provided in at least one side zone arranged on each side of the central zone.
 14. The method according to claim 12, wherein a first local suction is provided in an outermost side zone arranged at a side edge of the at least one vacuum box, and where the first local suction is independently controlled in relation to a second local suction provided in at least one side zone arranged adjacent to the outermost side zone. 